(a) Field of the Invention
The present invention relates to a tension device, and more particularly to a thread tension device for a sewing machine.
(b) Description of the Prior Art
A typical thread tension device which is commercially available at present is shown in FIG. 7 and comprises a bolt 90 having one end rotatably engaged in the front portion of a sewing machine 91 and having a knob 92 fixed on the other end by a bolt 93, the knob 92 includes a plurality of teeth 94 formed longitudinally therein, a follower 95 is threadedly engaged on the bolt 90 and includes a plurality of teeth formed on the outer peripheral portion thereof for engagement with the teeth 94 of the knob 92 such that the follower 95 can be rotated by the knob 92 and such that the follower 95 can be caused to move longitudinally along the bolt 90, a pair of discs 96 are engaged on the bolt 90 for clamping a thread 97, a spring 98 is biased between the follower 95 and the discs 96 for biasing the discs 96 together in order to clamp the thread 97, the follower 95 can be caused to force or to release the spring 98 when the knob 92 is rotated such that the resilient force of the spring 98 applied to the discs 96 can be adjusted and such that the thread tension can be adjusted.
However, in order to prevent the spring 98 from being over-pressed, an annular groove 921 is formed in the knob 92, a pin element 99 is extended outward from the sewing machine 91 and has a free end engaged in the annular groove 921, and a stop 922 is formed in the annular groove 921 for engagement with the pin element 99 such that the knob 92 is limited to rotate for one turn only, this arises one problem. Before the suitable thread tension is regulated, the manufacturers and the users have to use try and error method to rotate the knob 92 and the follower 95 in order to adjust the thread tension, if the thread tension is not acceptable, the bolt 93 and the knob 92 should be removed in order to rotate the disc 95 for over one turn and should be assembled in place again. This is inconvenient.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional thread tension devices.